Nearly every scene in the first third of “Mary and Martha” is part of a big old set-up. You, the viewer, are going to have your heart busted up, but first the writer and director of this HBO movie need to get you to invest and care. They need to make you love the characters, to seduce you with cutesiness and happy innocence, all before the sorrow train pulls into the station. Every shot of that noble little boy with plaintive eyes, every mention of his passion for pizza, is booby-trapped; later they will spring at you and tug rather aggressively at your heartstrings.

“Mary and Martha,” which premieres Saturday night at 8, is a movie motivated by good intentions — always a difficult proposition. It was written, by Richard Curtis of “Notting Hill” and “Love Actually,” to increase awareness of the hundreds of thousands of preventable deaths from malaria every year. It contains some statistics, but it’s more of a straight-up emotional plea for attention and resources. But you know how these things often go — you cheer for the cause, but are you a bad person if you don’t appreciate the manipulative and glib way the movie was made? Do you have to like the movie if you support the cause? Alas, pity the poor critic who has to look like a malaria-loving fiend to do his job!

Essentially, “Mary and Martha” operates like an EZ-to-read Lifetime movie with HBO production values. It was directed by Phillip Noyce, of “Patriot Games” and “Dead Calm,” and it looks sharp as it travels from upper-middle-class Virginia to Mozambique. Hilary Swank plays Mary, whose only son, the endearing George (Lux Haney-Jardine), is getting bullied at school. Her solution is to take him from their Virginia suburb to Africa for a six-month mother-and-son trip — “the biggest adventure of our lives ever,” she promises him. They say goodbye to dad (Frank Grillo), meet oh-so-lovable locals including a driver who likes country music, and make fart jokes. And then, after a mosquito bite, the dreaded words from son to mother: “I’m not feeling great.”

Meanwhile, in England, Martha (Brenda Blethyn) sends her energetic and cheery only son, Ben (Sam Claflin), off to Mozambique, too, to work as a teacher. Ben is older than George, but he is adorable and innocent in his own way, as he idealistically teaches kids to count to 10 and love Nelson Mandela. The movie tends to condescend toward the people of Africa, as the big Westerners show up to help the cute locals, but it’s hard to resist Ben’s enthusiasm. Then he is also bitten by a mosquito, and, well, you know. The movie spends much less time with Martha and Ben than it does with Mary and George, fortunately, so that we don’t have to go down the same long path twice.

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The two devastated mothers finally meet by chance during visits to Mozambique, and they instantly connect over their losses. It’s the most convincing relationship in the movie, as they communicate without a lot of explanation. “Didn’t we get lucky, running into each other,” Martha says when they part. “Didn’t we,” Mary says. Their marriages have been strained with complex feelings of grief and blame, but they are tight. Next stop: activism, with Mary and Martha ultimately going to Washington to make their case about malaria and preventability to legislators. In the process, Mary reconnects with her cold father, played by James Woods.

“Mary and Martha” is fictional, but the characters have the blandness you generally find in docudramas. You never feel as though Swank and Blethyn are going through the motions; they are too good for that, and they seem committed. But “Mary and Martha” has such a boilerplate and simplistic story arc, particularly when they wind up showing photos of their children at an appropriations hearing in Congress, that their performances aren’t memorable. They are simply tools of persuasion in this facile entreaty.